The present invention relates generally to fuel injection systems and, more particularly, to a fuel rail for fuel injection of a two-phase fuel.
Fuel injection systems having a plurality of electrically actuated fuel injector valves (“injectors”) receiving fuel from a common fuel rail are known in the art. In these systems, fuel under pressure from a fuel pump is distributed to the individual injectors by means of a common fuel rail. Traditional common fuel rails have a single fuel inlet port and deliver fuel to the injectors in series. Fuel injection systems may be designed to inject single-phase fuels such as diesel and gasoline or two-phase fuels which commonly include fuels such as liquid propane gas, methane, ammonia, liquid natural gas, and combinations thereof.
Fuel injection systems that inject a two-phase fuel in a liquid phase (a “liquid-phase fuel injection system”) demonstrate superior engine power and cold start performance over fuel injection systems that inject a two-phase fuel in a vapor phase. Liquid-phase fuel injection systems do present challenges, however, such as that of keeping the two-phase fuel in a liquid phase at the point of injection. For example, in hot soak conditions (such as when the engine has been turned off but is still hot), the liquid two-phase fuel can vaporize in the fuel rail, resulting in an inherently lower density fuel charge at the fuel injectors. In such cases, the engine management system cannot typically distinguish between the liquid and vapor phase of the two-phase fuel and, therefore, will deliver inadequate fuel quantity when the engine is restarted. Some liquid phase fuel injection systems attempt to address this problem by first displacing fuel vapor from the fuel rail upon a restart. The time required for such displacement (the “purge time”) is typically in the range of twenty to thirty seconds which is undesirable in many applications. In some cases, the fuel vapor is displaced through the engine which can create undesirable emissions.
In addition to hot soak conditions, a two-phase fuel may transform into the vapor phase in a fuel rail if the pressure in the fuel rail drops too much as the fuel is delivered in series to each of the injectors. As a result, many traditional liquid two-phase-fuel injection systems are designed to run at high pressures which can reduce durability of the system, increase cost, and increase the difficulty of delivering the two-phase fuel in uniform quantities to the injectors.